Primary Enteric-type adenocarcinoma of the bladder managed with colon-type chemotherapy: A rare case and literature review.

Primary adenocarcinoma of the urinary bladder is the rarest form of urinary tract malignancy, accounting for less than 2% of bladder cancers in the United States. Adenocarcinomas of the bladder are extremely rare, with distinct histological features, and, due to their morphological similarity to colorectal adenocarcinoma, they pose a diagnostic challenge. We report the case of a 62-year-old male with a significant history of tobacco use who presented with gross hematuria and irritative voiding symptoms. Imaging revealed a mass involving the posterior and inferior bladder wall, and biopsy confirmed invasive bladder adenocarcinoma. Immunochemistry supported a primary bladder origin (CK7-, CK20+, CDX2+, positive membranous β-catenin). The patient declined radical cystectomy in favor of bladder-sparing trimodality therapy. He remained recurrence-free for five years before developing locally invasive recurrence requiring systemic chemotherapy. This case highlights the importance of distinguishing primary bladder adenocarcinoma from secondary colorectal involvement, emphasizing the need for care to be adapted to a patient's changing clinical needs.